1. Field of the Invention
This invention relates to activators of one or more proteins in the Wnt pathway, including activators of one or more Wnt proteins, and compositions comprising the same. More particularly, it concerns the use of a β-diketone, γ-diketone or γ-hydroxyketone or salts or analogs thereof, in the treatment of osteoporosis and osteoarthropathy; osteogenesis imperfecta, bone defects, bone fractures, periodontal disease, otosclerosis, wound healing, craniofacial defects, oncolytic bone disease, traumatic brain injuries related to the differentiation and development of the central nervous system, comprising Parkinson's disease, strokes, ischemic cerebral disease, epilepsy, Alzheimer's disease, depression, bipolar disorder, schizophrenia; eye diseases such as age related macular degeneration, diabetic macular edema or retinitis pigmentosa and diseases related to differentiation and growth of stem cell, comprising hair loss, hematopoiesis related diseases and tissue regeneration related diseases.
2. Description of the Related Art
The Wnt/β-catenin signaling pathway is essential in many biological processes. It regulates the fate of as-yet undeveloped cells in embryo form. The Wnt/β-catenin signaling pathway is essential to stem cell self-renewal and proliferation as well as the development of stem cells in adult organisms (e.g. skin cell, bone cell, liver cell, etc.) [Science (2002), 296(5573), 1644-1646]. The Wnt/β-catenin signaling pathway regulates development, morphology, proliferation, motility and cell fate [Annual Review of Cell and Developmental Biology (2004), 20, 781-810]. The Wnt/β-catenin signaling pathway has a central role in tumorigenesis and inappropriate activation of this system is observed in several human cancers [“Wnt Signaling in Human Cancer”, in Signal Transduction in Cancer (pp. 169-187). (2006) Springer]. Wnt/β-catenin was first described in humans as a protein which interacts with the cytoplasmic domain of E-cadherin and with Wnt/β-catenin, anchoring the cadherin complex to the actin cytoskeleton [Science (1991), 254(5036), 1359-1361]. Then, an additional role for mammalian Wnt/β-catenin was discovered; namely, as the key mediator of Wnt/β-catenin messaging.
In the presence of a Wnt ligand, if not inhibited by secreted antagonists, the Wnt ligand binds a frizzled (Fzd)/low density lipoprotein receptor related protein (LRP) complex, activating the cytoplasmic protein dishevelled (Dsh in Drosophila and Dvl in vertebrates). Precisely how Dsh/Dvl is activated is not fully understood, but phosphorylation by casein kinase 1 (CK1) and casein kinase 2 (CK2) have been suggested to be partly responsible [Proceedings of the National Academy of Sciences of the USA (1999), 96(22), 12548-12552]. Dsh/Dvl then inhibits the activity of the multiprotein complex (β-catenin-Axin-adenomatous polyposis coli (APC)-glycogen synthase kinase (GSK)-3β), which targets β-catenin by phosphorylation for degradation by the proteasome. Dsh/Dvl is suggested to bind CK1 and thereby inhibiting priming of β-catenin and indirectly preventing GSK-3β phosphorylation of β-catenin [Genes & Development (2002), 16(9), 1066-1076]. Upon Wnt stimulation, Dvl has also been shown to recruit GSK-3 binding protein (GBP) to the multiprotein complex. GBP might titrate GSK-3β from Axin and in this way inhibits phosphorylation of β-catenin. Finally, sequestration of Axin at the cell membrane by LRP has been described [Molecular cell (2001), 7(4), 801-809]. The overall result is accumulation of cytosolic β-catenin. Stabilized β-catenin will then translocate into the nucleus and bind to members of the T-cell factor (Tcf)/Lymphoid enhancing factor (Lef) family of DNA binding proteins leading to transcription of Wnt target genes.
In the absence of a Wnt ligand, Axin recruits CK1 to the multiprotein complex causing priming of β-catenin and initiation of the β-catenin phosphorylation cascade performed by GSK-3β. Phosphorylated β-catenin is then recognized by β-transducin repeat-containing protein (β-TrCP) and degraded by the proteasome, reducing the level of cytosolic β-catenin.
Aberrant activation of the Wnt/β-catenin pathway has led to several phenotypes, including the development of a variety of human cancers, and diseases leading to abnormal development and functioning of the stem cells [Oncogene (2009), 28(21), 2163-2172; Cancer Cell (2008), 14(6), 471-484; American Journal of Pathology (2003), 162(5), 1495-1502]. Chronic activation of the Wnt/β-catenin signaling pathway has been implicated in the development of a variety of human malignancies, including high bone mass syndrome, sclerosteosis, colorectal carcinomas, hepatocellular carcinomas (HCCs), ovarian, uterine, pancreatic carcinomas, and melanomas [BioEssays (1999) 21(12), 1021-1030; Cell (2000), 103(2), 311-320; Genes Dev. (2000), 14(15), 1837-1851]. Since the Wnt/β-catenin pathway is involved in myriad growth and development processes, mutation of the proteins involved in the Wnt/β-catenin signal transduction system is closely correlated with various human diseases such as abnormalities in development, hair follicle morphogenesis, stem cell differentiation, bone formation and cell proliferation.
Hair Loss
Hair forms in a pouch-like structure below the skin called a hair follicle. Visible hair, for example that seen on a human scalp, is actually the hair shaft, which is keratinized, hardened tissue that grows from the hair follicle. In particular, the hair shaft is composed largely of keratin, which is produced by keratinocytes.
Normal hair follicles cycle between a growth stage (anagen), a degenerative stage (catagen), and a resting stage (telogen). Scalp hairs have a relatively long life cycle: the anagen stage ranges from 2 to 6 years, the catagen stage ranges from a few days to a few weeks, and the telogen stage is approximately three months. Shorter hairs found elsewhere on the human body have corresponding shorter anagen durations. The morphology of the hair and the hair follicle change dramatically over the course of the life cycle of the hair [Dermatology in General Medicine (Vol. I), McGraw-Hill, Inc., 1993, pp. 290-91; Sperling, L. C.; J. Amer. Acad. Dermatology (1991), 25(1, Part 1), 1-17].
During anagen, the hair follicle is highly active metabolically. The follicle comprises a dermal papilla at the base of the follicle; and epidermal matrix cells surrounding the dermal papilla form the base of the hair shaft, which extends upwards from the papilla through the hair canal. The matrix cells are the actively growing portion of the hair.
At catagen, the matrix cells retract from the papilla, and other degenerative changes occur. For example, the vessels and capillaries supplying blood and nutrients to the hair follicle shrivel and stop functioning. A column of epithelial cells pushes the keratinized proximal shaft of the hair upwards, and cell death occurs within the follicle. The hair shaft is then shed from the scalp or other part of the body and the hair follicle enters telogen, the resting stage of the hair growth cycle.
Although hair follicle regulation and growth are not well understood, they represent dynamic processes of proliferation, differentiation, and cellular interactions during tissue morphogenesis. It is believed that hair follicles are formed only in the early stages of development and are not replaced. Thus, an increase in damaged or non-functioning hair follicles is generally associated with hair loss.
Male or female pattern baldness requires the presence of male or female hormones, e.g. androgens, but the cause is unknown. The extent of hair loss in any male greatly depends on the genes he inherits from his father, mother, or both. Hair loss begins at the temples or at the top of the head. If male pattern hair loss begins in the mid-teens, subsequent hair loss is usually fairly extensive. Male balding goes in waves. Hair loss may begin in the early 20's, then stop, only to start again in a few years. By the age of 20 to 30 years, 30% of men have bald spots. This continues to rise until age 50-60, when 50% of men are completely bald.
The rate of hair loss is affected by advancing age, the tendency to bald early due to inherited genes, and an overabundance of the male hormone dihydrotestosterone (DHT) within the hair follicle. DHT acts on a hormone receptor within the hair follicle, and thereby slows hair production and produces weak, shorter hair. Sometimes DHT production even stops hair growth completely. Although balding men have above average amounts of DHT in their hair follicles, they usually do not have above average circulating testosterone levels.
Female pattern baldness is not as common as male pattern baldness, but is on the rise. It is confined to the hair predominantly at the top of the head and complete baldness is rare in females.
Toxic alopecia is temporary but typically lasts three to four months, and often is caused by an infectious disease. For example, toxic alopecia may occur as a result of hypothyroidism, diabetes, hormonal problems, vitamin deficiencies, hypopituitarism, parasites, poor digestion, early stage of syphilis, vitamin A or retinoid overdoses, or other cytotoxic drugs.
Alopecia greata is a sudden hair loss in demarcated areas. It can affect any hairy area, but most frequently affects the scalp and beard. Hair loss confined to a few areas is often reversed in a few months even without treatment but recurrence is a possibility. Alopecia greata usually occurs in people with no obvious skin disease or systemic disease, but in rare cases lab tests may show anti-microsomal antibodies to thyroglobulin, gastric parietal cells and adrenal cells.
Scarring alopecia results from inflammation and tissue destruction. It may be due to injuries such as burns, physical trauma, or destruction after x-rays. In these cases, little regrowth is expected. Other causes are cutaneous lupus erythematosus, lichen planus, chronic deep bacterial or fungal infections, deep ulcers, sarcoidosis, syphilis, or tuberculosis. Slow growing tumors of the scalp are a rare cause of hair loss.
While none of these conditions is very well understood, each condition is distressing because hair is often considered an important factor in human social communications and interactions.
Numerous approaches have been suggested for treating hair loss. Two of the most commonly used and accepted compounds for preventing hair loss are minoxidil, the active ingredient in Rogaine® and the 5α-reductase inhibitor, finasteride, the active ingredient in Propecia®. However, cosmetic treatment of age-related hair loss in patients with topical solution of minoxidil or finasteride has resulted in only moderate regrowth of hair in less than 40% of such patients. Indeed, less than ten percent of the men who use Rogaine® achieve satisfactory results. Thus, there is a need in the art for more effective methods of, and compositions for treating hair loss. Preferably, new methods and compositions will require fewer applications of active ingredients; provide hair regrowth sooner, in more abundance, and thicker, than presently observed with minoxidil or finasteride treatment.
It has been found that hair follicle development and regeneration are regulated by the canonical Wnt/β-catenin signaling pathway [Investigative Dermatology (2008), 128(5), 1081-1087]. In the epidermis, hair follicle development is initiated when mesenchymal cells populate the skin. During this process, signals emanating from the dermis induce epithelium thickening, elongation of the epithelial cells, and the formation of placodes containing Wnt-responsive cells. In response, placodes signal dermal cells to condense, thereby forming the dermal papilla component of the hair follicle, which is also responsive to Wnt signaling Wnt3a is secreted from hair epithelium and acts in an autocrine and paracrine fashion, and it has been demonstrated that Wnt-3a maintains anagen gene expression in dermal papilla cells and mediates hair-inductive activity in an organ culture. This Wnt-3a-mediated hair growth might depend on the canonical Wnt/β-catenin signaling pathway because deletion of β-catenin or the Lef1 gene resulted in hair loss in mice. Therefore, activation of β-catenin by Wnt contributes to the inhibition of keratinocytes differentiation, induction of hair follicle formation, and maintenance of proliferation of neuronal progenitors.
Neurodegenerative Diseases
Neurodegenerative diseases result from deterioration of neurons or their myelin sheath which over time will lead to dysfunction and disabilities resulting from this. Adult mammalian brain has limited capacity for regeneration. This makes the repair of any injuries hazardous and, consequently, CNS traumas are devastating.
New neurons are generated from neural stem cells, in two regions of the adult mammalian central nervous system: the subventricular zone of the lateral ventricle, and the subgranular zone of the hippocampal dentate gyrus [Current Opinion in Cell Biology (2001), 13, 666-672]. Signals provided by the microenvironment contribute to the regulation of the maintenance, proliferation and neuronal fate commitment of the local stem cells. Many of these signals and signaling pathways are unknown.
Alzheimer's disease (AD) is the most common cause of dementia that gradually destroys neurons and affects more than 24 million people worldwide. It occurs mostly in older adults and patients afflicted with AD lose their ability to learn, remember, make decisions, communicate and carry out daily activities. The etiology and progression of AD is not well understood, but is associated with amyloid beta (Aβ) plaques and neurofibrillary tangles in the brain.
Parkinson's disease (PD) is a degenerative disorder of the central nervous system affecting more than 6 million people worldwide and that often impairs the sufferer's motor skills and speech. The symptoms of Parkinson's disease result from the loss of dopamine-secreting cells in the region of the substantia nigra (literally “black substance”). These neurons project to the striatum and their loss leads to alterations in the activity of the neural circuits within the basal ganglia that regulate movement.
Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease that results from the death of motor neurons. A progressive loss of muscle control impairs the individual's capacity for independent function. ALS strikes the cells in the brain and spinal cord (motor neurons), which send signals to move muscles. In some cases, a mutation in the SOD1 gene results in a dysfunctional protein, the superoxide dismutase protein (called SOD1), which normally “cleans” up toxic particles inside a cell. When SOD1 is mutated, toxic particles accumulate inside motor neurons causing them to malfunction. But this mutation only explains a few percent of cases of ALS. The primary cause of ALS, which afflicts about 350,000 adults worldwide, is unknown.
Stroke and traumatic brain injury can also cause neuronal loss and lead to cognitive decline. Stroke can be classified into two major categories: ischemic and hemorrhagic. Ischemia is due to interruption of the blood supply, while hemorrhage is due to rupture of a blood vessel or an abnormal vascular structure. Stroke can cause permanent neurological damage, complications and death if not promptly diagnosed and treated. It is the third leading cause of death and the leading cause of adult disability in the United States and Europe.
Frontotemporal Dementia (FTD) accounts for 18% of dementias in people under 65 years old. It frequently manifests itself as a behavioral disturbance, and can progress to impair an individual's capacity for independent thought and function. Recent studies have uncovered genetic factors that contribute to this dementia; however no treatment yet exists to block the brain deterioration it causes.
Wnt/β-catenin signal transduction system plays a crucial role in the differentiation and development of nerve cells for the central nervous system, suggesting a relationship between Wnt/β-catenin proteins and the incidence of various diseases of the central nervous system, including neurodegenerative diseases [Nature (2005), 437(7063), 1370-1375]. Particularly, it is also found that Wnt/β-catenin signaling is related to diseases resulting from the abnormality of nerve cells, such as brain damage, Parkinson's disease, Amyotrophic Lateral Sclerosis (Lou Gehrig's disease), stroke, epilepsy, Alzheimer's disease (AD), depression, bipolar disorder, and schizophrenia.
Alzheimer's disease is the most common age-related neurodegenerative disorder. In fact, a relationship between amyloid-β-peptide (Aβ)-induced neurotoxicity and a decrease in the cytoplasmic levels of β-catenin has been observed. Apparently Aβ binds to the extracellular cysteine-rich domain of the Frizzled receptor (Fz) inhibiting Wnt/β-catenin signaling. Cross-talk with other signaling cascades that regulate Wnt/β-catenin signaling, including the activation of M1 muscarinic receptor and PKC, the use of Ibuprofen-ChE bi-functional compounds, PPAR α, γ agonists, nicotine and some antioxidants, results in neuroprotection against Aβ. These studies indicate that a sustained loss of Wnt signaling function may be involved in the Aβ-dependent neurodegeneration observed in Alzheimer's brain. Thus, the activation of the Wnt/β-catenin signaling pathway could be proposed as a therapeutic target for the treatment of AD.
Eye Diseases
Age related macular degeneration (AMD) is a medical condition which usually affects older adults that results in a loss of vision in the center of the visual field (the macula) because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of visual impairment in older adults (>50 years). The inner layer of the eye is the retina, which contains nerves that communicate sight, and behind the retina is the choroid, which contains the blood supply to the macula (the central part of the retina). In the dry (nonexudative) form, cellular debris called drusen accumulate between the retina and the choroid, and the retina can become detached. In the wet (exudative) form, which is more severe, blood vessels grow up from the choroid behind the retina, and the retina can also become detached. It can be treated with laser coagulation, and with medication that stops and sometimes reverses the growth of blood vessels.
Diabetic retinopathy is retinopathy (damage to the retina) caused by complications of diabetes mellitus, which can eventually lead to blindness. It is an ocular manifestation of systemic disease which affects up to 80% of all patients who have had diabetes for 10 years or more. As new blood vessels form at the back of the eye as a part of proliferative diabetic retinopathy (PDR), they can bleed (hemorrhage) and blur vision. Some people develop a condition called macular edema. It occurs when the damaged blood vessels leak fluid and lipids onto the macula, the part of the retina that lets us see detail. As the disease progresses, severe nonproliferative diabetic retinopathy enters an advanced, or proliferative, stage. The lack of oxygen in the retina causes fragile, new, blood vessels to grow along the retina and in the clear, gel-like vitreous humour that fills the inside of the eye. Without timely treatment, these new blood vessels can bleed, cloud vision, and destroy the retina.
Retinitis pigmentosa (RP) is a group of genetic eye conditions. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some sight all their lives [American Journal of Ophthalmology (2003), 136(4), 678-68]. Others go completely blind from RP, in some cases as early as childhood. Progression of RP is different in each case. RP is a type of progressive retinal dystrophy, a group of inherited disorders in which abnormalities of the photoreceptors (rods and cones) or the retinal pigment epithelium (RPE) of the retina lead to progressive visual loss. Affected individuals first experience defective dark adaptation or nyctalopia (night blindness), followed by reduction of the peripheral visual field (known as tunnel vision) and, sometimes, loss of central vision late in the course of the disease.
Müller glia, or Müller cells, are glial cells found in the vertebrate retina, which normally serve the functions of any normal glial cells. However, following injury to the retina, it has been seen that Müller glia undergo dedifferentiation into multipotent progenitor cells. At this point, the progenitor cell can divide and differentiate into a number of retinal cell types, including photoreceptors, that may have been damaged during injury. Additionally, recently published research has shown that Müller cells act as a light collector in the mammalian eye, analogous to a fiber optic plate, funneling light to the rod and cone cells.
Multipotent retinal progenitors must solve two fundamental problems. First, they must initially expand their numbers but later limit their proliferation so that the right number of differentiated cells is produced at the appropriate developmental time. Second, the distinct processes of division and differentiation must be coordinated so that differentiation can be initiated when cells stop dividing [Current Opinion in Genetics & Development (1997), 7(5), 651-658; Nature Reviews Neuroscience (2001), (2), 109-118]. Wnt promotes cell proliferation in multiple tissues [Cell and Tissue Research (2008), 331(1), 193-210], in particular in the developing retina [Stem Cells (2008), 26(8), 2063-2074; Development (2003), 130(3), 587-598; Development (2005), 132(12), 2759-2770; Development (2005), 132(13), 3027-3043]. The SoxB1 family of genes (Sox1-3) may be key effectors of Wnt/β-catenin signaling in the developing nervous system [Development (2006), 133(22), 4451-4461; Neuron (2005), 46(1), 23-36]. During neurogenesis, Sox2 antagonizes proneural genes and can maintain progenitors [Nature Neuroscience (2003), (6), 1162-1168; Neuron (2003), 39(5), 749-765]. In the frog retina, Wnt/β-catenin signaling through Fz5 is necessary for Sox2 expression, which is required for proneural gene expression and the transition from progenitors to neurons [Neuron (2005), 46(1), 23-36]. It was discovered that these factors are core components of a conserved hierarchical cascade and propose that they form a powerful directional network that drives cells from a proliferative, undifferentiated state to a nonproliferative, differentiated neuronal or glial fate [Development (2009), 136(19), 3289-3299].
Regeneration in the mammalian CNS is severely limited. Unlike in the chick, current models hold that retinal neurons are never regenerated. It has been demonstrated that, in the adult mammalian retina, Miller glia dedifferentiate and produce retinal cells, including photoreceptors, after acute neurotoxic injury in vivo. However, the number of newly generated retinal neurons is very limited. It has been demonstrated that Wnt/β-catenin signaling promotes proliferation of Müller glia-derived retinal progenitors and neural regeneration after damage or during degeneration. Wnt3a treatment increases proliferation of dedifferentiated Müller glia>20-fold in the photoreceptor-damaged retina. It has also been shown that in the degenerating retina, Wnt3a increased cell proliferation, and treatment with RA or VPA promoted the differentiation of these cells into rhodopsin-positive photoreceptor cells [Journal of Neuroscience (2007), 27(15), 4210-4219].
Therefore, we propose that modulating the Wnt/β-catenin pathway is one possible therapeutic strategy to enhance replacement of lost neurons by generating cells derived from endogenous neuronal progenitors.
Bone Formation
Canonical Wnt/β-catenin signaling has been demonstrated to increase bone formation, and Wnt pathway components are being pursued as potential drug targets for osteoporosis and other metabolic bone diseases [Bone (2009), 44(6), 1063-1068]. In modern times, bone diseases are increasing due to socio-environmental and genetic factors, particularly due to increase of population of elderly persons. Generally, bone diseases occur and develop without special symptoms, and rapidly worsen with age. Although many drugs have been developed for the treatment of bone diseases thus far, most of them mainly aim to alleviate pain or to retard the decrease of bone density. They are not effective as a curative medication which aims for increasing the bone density of patients who suffer from osteoporosis. Some other drugs are usually in the form of injections and are reported to produce side effects upon long-term administration thereof.
Signaling through the Wnt/β-catenin pathway can increase bone mass through a number of mechanisms, including renewal of stem cells, stimulation of preosteoblast replication, induction of osteoblastogenesis, and inhibition of osteoblast and osteocyte apoptosis. One molecular mechanism is through the stimulation of the Wnt pathway by Wnt-3a interaction of its receptors LRP5 and Fzd [Journal of Medicinal Chemistry (2009), 52(22), 6962-6965]. Bone forming osteoblasts express the proteins LRP5 and Fzd on the surface membrane, which serve as co-receptors for the soluble peptide agonist Wnt-3a. Once stimulated with Wnt-3a, internal concentrations of free f3-catenin rise and enter the nucleus and recruit T-cell factor (TCF). Transcriptional events follow and result in the production of additional anabolic gene products. An additional soluble extracellular protein, Dkk-1, antagonizes this process by simultaneously binding to the cell surface receptors Kr2 and LRP5, effectively inhibiting Wnt-3a binding to LRP5. In addition, the Kr2/LRP5/Dkk-1 complex undergoes endocytosis to remove LRP5 from the cell membrane, thereby nullifying its function. Loss-of-function mutations of secreted Wnt antagonists like Dkk-1, SOST/sclerostin and secreted frizzled-related protein (sFRP)-1 result in increased bone formation due to changes in a variety of osteoblast parameters like proliferation, differentiation, recruitment/longevity and function [Journal of Bone and Mineral Research (2009), 21(6), 934-945], while deletion of the β-catenin-activated transcription factor TCF-1 causes osteopenia that arises from a reduction in osteoprotegerin expression by the osteoblast [Developmental Cell (2005), 8(5), 751-764].
Intestinal Diseases
The adult intestinal epithelium is characterized by continuous replacement of epithelial cells through a stereotyped cycle of cell division, differentiation, migration and exfoliation occurring during a 5-7 day crypt/villus transit time. The putative growth factors regulating proliferation within the adult intestinal stem cell niche have not yet been identified, although studies have implicated the cell-intrinsic action of β-catenin/Lef/Tcf signaling within the proliferative crypt compartment.
A number of pathological conditions affect the cells of the intestines. Inflammatory bowel disease (IBD) can involve either or both the small and large bowel. Crohn's disease and ulcerative colitis are the best-known forms of IBD, and both fall into the category of “idiopathic” inflammatory bowel disease because the etiology for them is unknown. “Active” IBD is characterized by acute inflammation. “Chronic” IBD is characterized by architectural changes of crypt distortion and scarring. Crypt abscesses can occur in many forms of IBD.
Ulcerative colitis (UC) involves the colon as a diffuse mucosal disease with distal predominance. The rectum is virtually always involved, and additional portions of colon may be involved extending proximally from the rectum in a continuous pattern. The etiology for UC is unknown. Patients with prolonged UC are at increased risk for developing colon cancer.
Patients with UC are also at risk for development of liver diseases including sclerosing cholangitis and bile duct carcinoma.
Crohn's disease can involve any part of the GI tract, but most frequently involves the distal small bowel and colon. Inflammation is typically transmural and can produce anything from a small ulcer over a lymphoid follicle (aphthoid ulcer) to a deep fissuring ulcer to transmural scarring and chronic inflammation. One third of cases have granulomas, and extracolonic sites such as lymph nodes, liver, and joints may also have granulomas. The transmural inflammation leads to the development of fistulas between loops of bowel and other structures. Inflammation is typically segmental with involved bowel separating areas of involved bowel. The etiology is unknown, though infectious and immunologic mechanisms have been proposed.
Gluten, a common dietary protein present in wheat, barley and rye causes a disease called Celiac disease in sensitive individuals. Ingestion of such proteins by sensitive individuals produces flattening of the normally luxurious, rug-like, epithelial lining of the small intestine.
Other clinical symptoms of Celiac disease include fatigue, chronic diarrhea, malabsorption of nutrients, weight loss, abdominal distension, anemia, as well as-a substantially enhanced risk for the development of osteoporosis and intestinal malignancies such as lymphoma and carcinoma. Celiac disease is generally considered to be an autoimmune disease and the antibodies found in the serum of the patients support the theory that the disease is immunological in nature.
Transgenic mice that have a knock-out of the Tcf locus show a loss of proliferative stem cell compartments in the small intestine during late embryogenesis [Oncogene (2006) 25(57), 7512-7521]. However, the knockout is lethal, and so has not been studied in adults. In chimeric transgenic mice that allow analysis of adults, expression of constitutively active NH2-truncated p-catenin stimulated proliferation in small intestine crypts, although either NH2-truncated p-catenin or Lef-1/□-catenin fusions induced increased crypt apoptosis as well [The Journal of Cell Biology (1998), 141(3), 765-777; The Journal of Biological Chemistry (2002), 277(18), 15843-15850]. Because diverse factors regulate P-catenin/Lef/Tcf-dependent transcription, including non-Frizzled GPCRs and PTEN/PI-3-kinase, the cause of intestinal stem cell defect is not known. Genes expressed in the gastrointestinal tract that are controlled by Wnt/β-catenin include CD44, and EphB2.
Regenerative Medicine
Due to the remarkable advances made in the field of medicine in recent years, opportunities for saving lives are continuing to increase in the area of living donor transplant techniques for tissues and organs. However, there are limitations on treatment dependent upon living donor transplants due to such factors as a shortage of transplant donors and the occurrence of rejection. If it were possible to regenerate a tissue or organ that has been lost due to surgical treatment or an unforeseen accident, then it would be possible to considerably improve the quality of life for patients. In addition, regenerative medicine also makes it possible to resolve the problems confronting living donor transplants. From this viewpoint, the degree of expectations being placed on regenerative medicine is high.
Technologies in which regenerative medicine has been successful are primarily related to comparatively simple tissue in terms of morphology or function in the manner of artificial skin, artificial bone and artificial teeth. Reconstructed artificial skin and artificial bone is incorporated into cells enabling the providing of signals required for tissue construction. However, there have been limitations on the repertoire of differentiation of artificial skin and artificial bone by regenerative medicine techniques. For example, although allogeneic keratinocytes or skin fibroblasts and the like differentiate into structures in the form of the epidermis, are incorporated by surrounding organs to eventually have a horny layer or basal layer having barrier properties, there has been reported to be no derivation of secondary derivatives such as hair follicles, sebaceous glands or sweat glands.
Body tissue normally contains both cells that are able to self-replicate and possess stem cell properties for maintaining tissue homeostasis by sending signals to differentiated cells or supplying differentiated cells, and cells having properties of somatic cells that have already differentiated that receive various signals or commands from such cells, and is able to function through interaction between both of these types of cells. In the case of vertebrates, for example, interaction between mesenchymal cells and epithelial cells is essential for nearly all tissue and organ formation. In the case of hair follicles, mesenchymal cells in the form of hair papilla cells are responsible for stem cell-like properties, while epithelial cells in the form of keratinocytes are equivalent to cells having somatic cell-like properties in their ability to differentiate into hair shafts (hair itself).
The difficulty encountered when forming organs by regenerative medicine lies in reaching a state of coexistence between cells having stem cell-like properties maintained in an undifferentiated state and cells that have already differentiated as in actual body tissue. In the prior art, even if epithelial cells and mesenchymal cells were able to be co-cultured, they either both ended up differentiating or both maintained an undifferentiated state, thereby preventing the reproduction of the coexistence of undifferentiated cells and differentiated cells so as to mimic actual body tissue.
Guiding multipotent cells into distinct lineages and controlling their expansion remain fundamental challenges in developmental and stem cell biol. Members of the Wnt pathway control many pivotal embryonic events, including self-renewal or expansion of progenitor cells.
Published observations suggest that canonical Wnt signals play distinct roles during discrete developmental windows, first positively regulating mesoderm commitment and then possibly playing a negative role in the initial induction of cardiac progenitors [Genes & Development (2001), 15(3), 316-327; Ibid., 304-315; Proc Natl Acad Sci USA. (2006), 103(52), 19812-19817; Development (Cambridge, UK) (2006), 133(19), 3787-3796]. The loss- and gain-of-function studies of canonical Wnt signaling in a spatiotemporally restricted manner described here provide compelling evidence that Wnt/β-catenin signaling is required in a cell autonomous fashion for the expansion and development of precardiac mesoderm and cardiac mesoderm in mouse. Thus, narrow developmental windows may exist during which canonical Wnt signaling sequentially inhibits then promotes cardiac development. Thus it was shown that canonical Wnt signaling can be manipulated to regulate expansion and differentiation of progenitor cells.
In contrast to progenitor cells, however, stem cells are far less specific. The most important difference between stem cells and progenitor cells is that stem cells can replicate indefinitely, whereas progenitor cells can only divide a limited number of times. The term adult stem cell, also known as somatic and gametes, refers to any cell which is found in a developed organism that has two properties: the ability to divide and create another cell like itself and also divide and create a cell more differentiated than itself. They can be found in children, as well as adults [Nature (2002), 418(6893), 41-49]. All somatic cells of an individual are genetically identical in principle, they evolve a variety of tissue-specific characteristics during the process of differentiation, through epigenetic and regulatory alterations. Pluripotent somatic stem cells are rare and generally small in number but can be found in a number of tissues including umbilical cord blood. A great deal of somatic stem cell research has focused on clarifying their capacity to divide or self-renew indefinitely and their differentiation potential. In mice, pluripotent stem cells are directly generated from adult fibroblast cultures. Unfortunately, many mice don't live long with stem cell organs.
Somatic cells can be reprogrammed to induced pluripotent stem cells (iPSC) by retroviral transduction of four transcription factors [Cell (2008), 132(4), 567-582]. While the reprogrammed pluripotent cells are thought to have great potential for regenerative medicine [Proc. Natl. Acad. Sci. USA (2008), 105(15), 5856-5861], genomic integrations of the retroviruses, especially c-Myc, increase the risk of tumorigenesis [Nature (2007), 448(7151), 313-317]. Generation of iPSCs for use in the clinical setting would benefit from identification of alternative, ultimately safer, initiating stimuli, in preference to genetic modification. This could be transient treatment with defined factors, low-toxicity chemicals, or synthetic small molecules. Since the Wnt pathway is intimately connected to the core circuitry of pluripotency, it has been shown that the stimulation of the pathway using soluble Wnt3a promotes the generation of iPSCs in the absence of c-Myc retrovirus. These data demonstrate that signal transduction pathways and transcription factors can act coordinately to reprogram differentiated cells to a pluripotent state [Cell Stem Cell (2008), 3(2), 132-135; Cell Stem Cell (2008), 3(5), 465-466].
As discussed above, activators of the Wnt/β-catenin signaling pathway are expected to be medicaments useful against cell proliferation disorders, bone disorders, eye diseases, Alzheimer's disease and even tissue generation. Thus, it would be advantageous to have novel activators of the Wnt/β-catenin signaling pathway as potential treatment regimens for Wnt/β-catenin signaling pathway-related disorders. The instant invention is directed to these and other important ends.